1. Field of the Invention
The present invention relates to a bonding inspection structure.
2. Description of Related Art
In the process of chip-on-glass (COG) bonding, a bonding gap between glass and an IC is determined by factors, such as pressure for the fabrication, characteristics of the materials, release of stress, and so forth. A typical method for inspecting the bonding quality is to observe the compression of conductive particles of an anisotropic conductive film (ACF). When improper compression occurs, the conductive particles are not cracked, which easily fails in the conductivity of electricity. However, if the compression pressure is overly high and excessively compresses the conductive particles, non-conductivity may also occur.
To achieve high density of contacts, materials, such as elastic bumps and non-conductive films (NCF), tend to be used in the design of IC bumps. Although there are no conductive particles of the anisotropic conductive film (ACF) for observation, compressed elastic bumps have characteristics similar to compressed conductive particles and the cracking of the elastic bumps can also be used to inspect the bonding quality. The cracking of elastic bumps can only be analyzed by using a scanning electron microscope (SEM). Hence, the inspection of compression and conductivity can only be performed based on slices thereof and flexible board testing after the fabrication is completed.
The disclosures of U.S. Pat. No. 5,707,902 and U.S. Pat. No. 6,972,490 are related to bonding inspection. U.S. Pat. No. 5,707,902 is focused on improving the shape, size, and arrangement of bumps, and the inspection is based on compression traces. However, the bumps in the aforesaid patent do not allow the inspector to instantly and effectively examine the height difference of bonding gap. Hence, the damage cannot be effectively detected. U.S. Pat. No. 6,972,490 discloses elastic bumps used as stoppers. The aforesaid elastic bumps all have the same height that is lower than electrode bumps. Thus, there is no damage or cracking for immediate inspection. In addition, this patent does not mention whether the bump structures can be conducted for determining the fabrication yield.